Fig. 4: Decoding scheme. | Communications Physics

Fig. 4: Decoding scheme.

From: Leveraging the orthogonality of Zernike modes for robust free-space optical communication

Fig. 4

Schematic of the decoding scheme at the receiving station: the wavefront from the transmission station is incident on a type-K modal wavefront sensor at the receiving station. The receiving station has a priori the key information regarding the Zernike modes used, such as Z6 and Z11 and their strengths, to design an appropriate type-K hologram (such as the one shown in the inset). For a given incident wavefront the type-K hologram generates a focal spot pattern, such as the one shown in the inset. The focal spot pattern is employed to obtain the sensor outputs for all the Zernike modes used during encoding. The type-K sensor outputs, such as b6 and b11, are first thresholded and then the ϕRMS values after thresholding (such as 0,  −0.5, or 0.5 radian) are converted to appropriate base-n digit using the lookup table (such as Table 1 for base-9). Thus, the receiving station a priory needs to have the lookup table. Each wavefront incident on the type-K sensor results in one digit of the base-n number system and base-n digits corresponding to all the wavefronts received at different time slots are converted to the user data.

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